\begin{tabular}{cccc}
	A     & B                         & C     & D                         \\
	AAA   & BBB                       & CCC   & DDD                       \\
	\multicolumn{2}{c}{first heading} & \multicolumn{2}{c}{second heading}\\
	one   & two                       & three & four                      \\
	five  &                           & six   &                           \\
	seven &                                                               \\
\end{tabular}
